Who should my next 5* upgrade be?

Hey guys, so I'm at an impasse. So I, as I assume some of the people here that have been playing this game for long enough, no longer have priority on any kind of units on which I need to upgrade. All the ones I have in consideration are ones I like equally and and have no pressing need to fit into any teams, so I'm a bit lost and made this thread via @Locky's suggestion and because I never post in the forums lol.

I'll include my unlock potential units in their barracks and which ones I have in consideration so if anyone has any advice/suggestion on which, please feel free.

1. Robin F
Thanks to the new meta of Reinhardts and Bolins (Brave Lyn lul) running around, Robin F becomes one of the few perfect counters to both the most currently popular units in arena. As you can see, I have her kit finished except for assist skill.

2. Frederick
I have the perfect IV Brave Frederick ready for upgrade. He does not have any of his skills, but I have the fodder for it and it's also a cheap build Brave Axe aside which he already has.

3. Anna
She's the only one of the Askr trio still 4*. I don't have her built at all nor do I have any idea how I would, but she's in consideration since Askr trios are always in arena bonus unit rotation.

4. Sheena
I've always like Sheena, but I don't have a particular build for her worked out yet nor the fodder I even would need for the builds I have in mind.

5. Robin M
Similar reason to Robin F, I've always wanted to 5* Robin M as well as F.

Honourable Mentions:
Hana - Perfect IV Brave Hana
Xander - Good unit, but I have an Eldigan built already.

Most of the units I have in consideration are coincidentally green, but it goes without saying that most of us have more red and blue units in abundance than green (aside colourless lol). If anyone has any suggestions or advice/tips, units they see listed they're fond of and have a good build on their own they want to share, please feel free. Thanks in advance for the contribution!

1. RobinF - immediate new meta concern and build is almost done.
2. Anna - because arena rotation. Please click this link, I'm lazy to repeat myself
3. RobinM - so you can make robin-selfcest ally support another meta counter
4. Frederick - because you already have the fodders.
5. Xander - he can be Eldigan's backup in assault mode
6. Hana - brave sword or wo dao Hana
7. Sheena - because you dont freaking have the fodder.

1. RobinF - immediate new meta concern and build is almost done.
2. Anna - because arena rotation. Please click this link, I'm lazy to repeat myself
3. RobinM - so you can make robin-selfcest ally support another meta counter
4. Frederick - because you already have the fodders.
5. Xander - he can be Eldigan's backup in assault mode
6. Hana - brave sword or wo dao Hana
7. Sheena - because you dont freaking have the fodder.

Click to expand...

Haha, yay so you're totally not against making a unit like Robin F 5*? Because some ppl prefer to keep her at 4.
And I like Sheena though D: I really do. But okay, thanksss~

I went with Robin F guys. I'll finish her out with x2 SP this weekend and show you all then. Thank you for the suggestions. I will most likely promote on from the rest of the list as @Locky suggested as it not only makes sense, but it's also the order I actually thought about when promoting these units. I just could never decide so the list built up and I became indecisive.

Although I really want to promote Sheena within the top 3, but don't have the fodder for her. T^T